Fix the upstream checkout and skip the dead cache server

Two separate CI failures:

- The cross-repo checkout of terraform-provider-dokploy asked the API
  for the default branch and got "not found", failing the build. An
  explicit ref: main skips the lookup entirely.
- setup-go caches by default, and this runner's cache server is
  unreachable from job containers, so restore and save each block until
  they time out. The same change cut the upstream provider's build from
  15m46s to 2m37s.

.gitea/workflows/build.yml

@@ -31,13 +31,16 @@ jobs:
           repository: ${{ env.UPSTREAM_REPO }}
           path: ${{ env.UPSTREAM_DIR }}
           token: ${{ secrets.GITEA_TOKEN }}
+          # Without an explicit ref, checkout asks the API for the default
+          # branch and fails on this Gitea with "not found".
+          ref: main
 
       - uses: actions/setup-go@v5
         with:
           go-version: ${{ env.GO_VERSION }}
-          cache-dependency-path: |
-            pulumi-dokploy/provider/go.sum
-            pulumi-dokploy/sdk/go.sum
+          # The runner's cache server is unreachable from job containers, so
+          # every restore/save hangs until timeout. Re-enable once fixed.
+          cache: false
 
       - uses: actions/setup-node@v4
         with: